Small-sized electric double layer capacitors of the coin type are in wide use for cellular phones, digital cameras and like electronic devices mainly as backup power sources. As is well known, the electric double layer capacitor of the coin type comprises a pair of polarizable electrodes having a separator interposed therebetween and housed in an inside space defined by a pair of metal cans arranged as insulated from and opposed to each other. The polarizable electrodes and the separator are impregnated with an aqueous or nonaqueous electrolyte.
For use on circuit boards, electronic components have been made in chip form in increasing quantities, so that rectangular areas are generally provided on circuit boards for mounting electric double layer capacitors thereon. However, if the coin-type electric double layer capacitor is provided in the rectangular mount area, the capacitor, which is in the form of a disk, leaves large vacant spaces at the corner portions of the mount area. For this reason, it is difficult to efficiently arrange various electronic components including the capacitor on the circuit board to be used for mounting the capacitor. Further in order to make the mounting step for circuit boards efficient, it is desired that the electric double layer capacitor be made in the form of a chip like other electronic components.
If the electric double layer capacitor is given a rectangular contour, the mount area can be utilized effectively with the vacant spaces diminished. Especially because a capacitor of increased size is then mountable, the capacitor so shaped has the advantage of being greater in capacity. However, when rectangular metal cans are used for conventional electric double layer capacitors, it is difficult to seal off the interstices between the metal cans with a gasket. Accordingly, study is under way for making containers from an insulating resin for use with electric double layer capacitors (see the publication of JP-A No. 2001-216952). The capacitor of the type mentioned can then be given a rectangular contour and made available in chip form.
FIGS. 13A to 13C are a perspective view and sectional views for illustrating an electric double layer capacitor having a resin container and an example of process for fabricating the same. As shown in FIG. 13A, a first container half segment 2 and a second container half segment 3, each box-shaped, are made first. Lead members 7, 8 each in the form of a flat plate are provided on the bottom walls defining recesses 20, 30. The container segments 2, 3 are made by insert molding, with the lead members 7, 8 extending through the respective segments 2, 3.
Next, these container segments 2, 3 are fitted together in combination as shown in FIG. 13B. At this time, a pair of polarizable electrodes 4, 5 and a separator 6, which are impregnated with an electrolyte, are arranged in superposed layers within a closed space defined by the container segments 2, 3 with the recesses 20, 30 facing toward each other. The electrodes 4, 5 are connected by current collecting members 9, 10 to the lead members 7, 8, respectively, and the separator 6 is interposed between the electrodes 4, 5.
Subsequently, the container segments 2, 3 are joined by ultrasonic welding to make a container 1. The platelike lead members 7, 8 are thereafter bent along the outer surface of the container 1 to position the outer ends of these lead members 7, 8 on the lower surface of the container 1. FIG. 13C shows the electric double layer capacitor completed by the above procedure and having the contour of a chip-type electronic component. The outer end portions of the lead members 7, 8 provide electrodes to be soldered when the capacitor is mounted on a circuit board.
Unlike other electronic components having a resin container, the electric double layer capacitor comprising a resin container internally has the polarizable electrodes and separator which are impregnated with an electrolyte. Accordingly, if the metal lead members 7, 8 extend through the container 1 as shown in FIG. 13C, the electrolyte is likely to leak to the outside by passing between the container 1 and the portions of the lead members 7, 8 embedded in the container 1 (arranged in the resin forming the container 1). Furthermore, the water ingressing into the container 1 from outside by passing between the container 1 and the lead members 7, 8 becomes mixed with the electrolyte and is likely to impair the performance of the capacitor.
When the lead members 7, 8 are bent in the process shown in FIGS. 13A to 13C, the force applied to these members 7, 8 is very likely to create an interstice between the container 1 and the lead members 7, 8. Additionally, the adhesion between the resin and the metal is generally low. To prevent the leakage of the electrolyte and the ingress of water, therefore, it is desired not to bend the lead members 7, 8 after the container segments 2, 3 are made by insert molding in fabricating the electric double layer capacitor having the resin container.
Further in order to prevent or diminish the leakage of the electrolyte and the ingress of water, it is effective that the path of flow of the electrolyte or water be elongated and complex. Because the electrolyte or water passes between the container 1 and the lead members 7, 8, it is desirable that the portions of the lead members 7, 8 embedded in the container 1 have the greatest possible length and be not straight.
Aqueous or nonaqueous electrolytic cells resemble electric double layer capacitors in construction, so that the fabrication of aqueous or nonaqueous electrolytic cells having a resin container also involves the above problem.
An object of the present invention is to overcome the above problem, to provide an electric double layer capacitor and an electrolytic cell which have a construction diminished in the likelihood of leakage of the electrolyte or ingress of water by allowing the liquid to pass between the container and the lead members, and to provide a process for fabricating these devices.